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jacko avatar image

AC coupled inverters that work with frequency shift (Solis?)

Hi Im after a list of brands that work with frequency shift to reduce output. Ive used fronius before that works well and ive heard SMA will aslo work, im wondering what other brands people have had success using, in particular im trying to find out if anyone has managed to use a Solis inverter as cost wise this would be great. Thanks

AC PV Couplingfrequency
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Phil Gavin avatar image
Phil Gavin answered ·

Yes, I have used a Solis on the AC out, and I can confirm frequency shifting works.

There are a number of national certifications that prescribe frequency shifting functionality, I tend just look for the VDE-4105 cerification.

On the otherhand, Fronius also has a "Micro-grid" setting which I believe adds something extra to stability during step load changes.

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Nice, thanks phill, does it work in a linear de-rating? As in not just on and off? Also what batteries are you using in the system that you have the solis connected to, I’m wondering how it would behave with lead acid after bulk and a tail off current is reached then float. I’ve used fronius primos in off grid and it doesn’t have the same functions as when connected into an ESS system where it’s is controlled without frequency but can still ramp down output rather than just switch it off

Matthew Walsh avatar image
Matthew Walsh answered ·

Am I correct that with pv inverters that support frequency shifting and are not natively controlled by the victron system (like fronius), the victron will only be able to control the pv load in an off grid situation? And when there is grid, the victron doesn't frequency shift which leads the non native pv inverter to produce its maximum avaiable pv which would result in feeding back excess pv to the grid?

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When the Victron MultiPlus ?Quattro is connected to the grid then of course it is not possible to frequency shift.
AC coupled PV power will feed loads and charge the battery. When the battery is full and loads are satisfied then excess will go back towards the grid.

Robert Bazalgette avatar image
Robert Bazalgette answered ·

Just completed install of the Solis PV 3 Kw inverter on the output of a new Victron ES II 3000 / 48v inverter, off grid system. Battery charging works well, but I STILL have an SOC issue with this inverter. It did not change the frequency even when the battery volts is at 56 v and the charge regualtor shows "Float" The inverter thinks the battery is at 85% SOC. I can't see in the inverter manual what it is using to determine the point at which to increase the frequency. I am assuming it is the SOC level. How do I get the inverter to agree with the charge regulator about the state of charge ?

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Hey there,

I have Fronius inverters AC-coupled with Quattros. I see frequency starting to shift at different SOC levels, below and above than 80%. First let's agree that SOC measurements are just calculations done by VE software based on voltage, Ah discharge/charge and are used in ESS to regulate discharge levels and sometimes turn on and off generators. But in case of AC-coupled battery charging, I believe dual inverter/chargers shift frequency based on electric sensing: meaning that the battery charging process is due to AC-out voltage rise from PV inverters and inverter responds to that if battery voltage has reached to a certain defined point. Unlike its normal 4-stage charging behavior when on-grid, I believe inverter/chargers cannot regulate charging normally when power is back fed through AC-out coupled PV invertrer. I think charging will be regulated by frequency shift when bulk voltage has reached, to prevent overcharging. And it will be done in one-stage.

I would suggest to look for VE.config file and check/change:

- General >battery monitor (typically SOC after bulk 85%, charging efficiency 0.8 if battery lead-acid)
- Charger tab > absorption and float voltages as per battery manufacturer recommendations
- ESS assistant > check PV inverter > adjust frequency limits as per Solis inverter grid parameters and country setup > total solar power

Note that continuous and repeated charging of batteries from an AC-coupled inverter is not ideal and is not recommended to sustain an acceptable battery lifetime and benefit from all potential energy throughput (lead-acid case).

It's always good to look at the country setup parameters set into Solis inverter to see the effect of frequency shift and its limits on PV output power (power reduction rate based on frequency). I use MG50 on my Fronius inverters. It is a universal MicroGrid specific set of code for 50Hz systems, it is best suited for off-grid ac-coupled systems.

Nazareth Kevorkian avatar image
Nazareth Kevorkian answered ·

Hi all,

I have systems using Growatt and Huawei grid-tie inverters AC-coupled with Quattro and MultiPlus. Anybody knows if the frequency shifting can work on these inverters as well?

As far as I understood from the Growatt people, the on-grid string inverter reacts to the reference network as the grid code installed suggests. So for example there is a specific curve for power ramp based on frequency variation on VDE-AR-N 4105. I guess the inverter would follow this regardless on how and why Quattro/Multi changes the frequency.

Note that I configured country grid code standard to be "Other: not compliant to any grid code standard".

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Chris avatar image
Chris answered ·

Can depend on the grid setup chosen as to what features are available.

However..... ive just come across a document by Solis for 50 /60Hz frequency derating control.

“Gen 50” or “Gen 60”

The default settings for “Generator 50” are Fstart – 51Hz (Start point of derating from 100% Prated, adjustable from 50Hz to 54Hz) Fstop – 52.7Hz (End point of derating to 0% Prated, adjustable from 50Hz to 54Hz)

May need a firmware update, but looks like its now properly supported.....

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Can you share the document that you came across please? Is this for a grid connected or off grid system? I'm interested in using the Solis for a grid connected system but I think the Fronius is the only one supported for this?

Phil Gavin avatar image
Phil Gavin answered ·

It ramps down the output as specified by VDE 4105 or whatever the country code you've set specifies.

Frequency power control is solely and off-grid feature. That is how I am using it. (Without ESS and with lead acid batteries)

Not that I have particularly looked into it, but:

I presume the output power is determined by whatever the AC loading is and the battery's DC demands. It appears as if the higher the battery voltage gets the more the output power is curtailed.

I further presume that the allowable battery voltage level is relative to the set charging voltage at that stage in the charging cycle.

In other words, the Victron limits the Solis through frequency to only provide the necessary extra to suit the charging cycle at the time, once the AC loads are covered.



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Yeah thats great thanks. Yeah aware frequency control can only be used in off grid as wouldnt be possible for battery inverter to change the frequency of the grid. I hoped this would be the case as you cant beat solis's prices fo grid tied inverters. Im from the UK so inverters will be sent out with G100 grid code hopfully the VDE 4105 apples to this grid code

Solis manuals arn't the best but these are prob the relevant parts